1. Field of Invention
The present invention relates to a display panel and the like, and more particularly, to the enhancement of visibility that is reduced due to the reflection of light incident from the exterior.
2. Description of Related Art
In the related art, display devices using a liquid crystal display (LCD) device or an organic electroluminescent element (hereinafter, referred to as an organic EL element) are employed in various electronic apparatus, such as a cellular phone, a personal computer, an electronic organizer, a portable electronic game console, and the like. As a result, users have many opportunities to look at a display screen for the electronic apparatus outdoors as well as indoors.
In this case, the light incident on the display screen from the exterior causes a problem. The incident light is reflected by the screen and viewed by viewers. Usually, more intense light is incident on the display screen outdoors than indoors and is reflected by the display screen to the viewers. As a result, the contrast of the display device is reduced, thereby making it difficult to see the display screen.
Herein, a related case where an organic EL element is employed will now be considered. Since the organic EL element is self-luminescent, it has a high visibility. Further, since its responsive speed is quick, the display device employing the element is a promising device to display a moving picture. However, with current organic EL elements, it is difficult to provide high luminance, while securing a long lifespan. Therefore, it is impossible to avoid a reduction in visibility outdoors due to the effect of light incident from the exterior.
Therefore, in order to enhance the contrast, a display device has been proposed in which anti-reflection films, including layered films of TiO2 and SiO2, are formed on the inner and outer surfaces of a cover to seal the display device (for example, see Japanese Unexamined Patent Application Publication No. 2001-230072). Further, another display device has been proposed in which a circular polarizer is mounted on a surface of the cover to suppress the reflection of the light incident from the exterior (for example, see Japanese Unexamined Patent Application Publication No. 8-321381). In addition, there is a case of achieving a high contrast by absorbing light using TaOx (tantalum oxide), which is deposited under a reactive atmosphere or by CVD, as an absorption layer (for example, see Japanese Patent No. 2901370). In addition, there has been proposed an organic EL element with an electric charge injecting layer having a light absorption diffusion property (for example, see Japanese Patent No. 2931229), a display panel with a black absorbent formed at a bottom side thereof (for example, see U.S. Pat. No. 5,986,401), or an organic EL element utilizing a black multi-layered film as the electrode (for example, see Japanese Unexamined Patent Application Publication No. 2003-17274).
However, in such related art display devices, since expensive equipment, such as a circular polarizer, must be attached to the display device, more expense and effort are required, thereby increasing its cost. In addition, there is a display device capable of suppressing reflectance by using a multi-layered film including three or more layers. But the structure and manufacturing method become complicated due to the plurality of films to be deposited.